This invention relates to the alloy art and has particular relationship to ferrous alloys of the ferritic type.
Plain carbon and low alloy ferritic steels and austenitic steels have poor creep resistance (Documents 1 and 2 above). Creep is defined as the progressive straining or deformation of material under a static load; creep is particularly significant at high temperatures typically about 1000.degree.F. When such materials are subjected to relatively low static tensile stress at elevated temperatures, they tend to elongate above amounts permissible in engineering designs. Rotating machines, for example steam turbine, component housings, and conductors operating at high temperatures (for example, 1050.degree.F), are typical of cases where creep must be limited. For such applications, 2.25%Cr-1%Mo steels have been used in accordance with the teachings of the prior art and the poor creep resistance of such steels has presented a serious problem because it was necessary to design components or parts such as housings and conductors so that the stresses imposed on them is low.
It is an object of this invention to provide alloy steel which shall permit design of such parts for higher stresses in high temperature service without exceeding, and indeed improving on, the presently obtained creep values resulting from the use of the Cr-Mo steel.
It is also an object of this invention to provide such an alloy which shall be no more costly than the presently used Cr-Mo steel and which shall be readily weldable without requiring high peheat temperatures, and shall be producible in both the cast and the wrought forms.